Commonly, such devices comprise two amplification stages arranged in series. The first stage is formed of a transistor-based preamplifier and the second stage of an electron tube. For this second stage, it is possible, for example, to use an inductive output tube well known in the literature by the abbreviation IOT. The output of the electron tube is linked to the transmit antenna.
The transistor-based preamplifier is generally installed in a control rack, which rack also comprises other units for forming a radiofrequency signal, which units are situated upstream of the preamplifier in the amplification chain. These other units also use transistors. The rack is generally cooled with air pulsed by means of fans.
The electron tube is, for its part, installed in its own enclosure and it can be cooled by the circulation of a fluid in the liquid state. This fluid comprises, for example, a glycol/water mixture.
The two amplification stages, the preamplifier and the electron tube, are generally made by separate equipment manufacturers. Specifically, the technical knowledge required to devise and make each of the two stages is very different. More precisely, the transistor-based preamplifier generally uses only low voltage (of the order of some 30 volts) and operates in ambient air. In contradistinction, the electron tube uses high voltages, certain voltages may exceed some 30 kilovolts. Moreover, the amplification carried out in an electron tube uses an electron beam traveling through an evacuated enclosure.
The separation of the two amplification stages poses problems of mutual compatibility. For example, the impedance matching between the preamplifier and the electron tube can be done only when the two stages are brought together at their place of use. Another example, a radiofrequency signal, already amplified by the preamplifier, flows through the cable linking the two stages. The linking cable generates losses proportional to the power of the radiofrequency signal and to the length of the cable itself. The separation of the two stages tends to increase the length of the linking cable and, consequently, the losses generated therein.
Furthermore, each of the two stages requires an individual cooling system, thereby increasing the risk of breakdown.
An aim of the invention is to reduce the above-mentioned drawbacks by proposing that the transistor-based preamplifier and the electron tube be grouped together.